All Podcasts / The Rest Is Science / Hacking The Kendama With Physics
The Rest Is Science
The Rest Is Science

Hacking The Kendama With Physics

September 30, 2026 • 40m

Summary

⏱️ 6 min read

Overview

Michael Stevens and Hannah Fry explore the physics of kendama (Japanese cup and ball toy) in this Field Notes episode. Michael brings Hannah a custom kendama made by Adam Savage using physics principles to make it easier to use, demonstrating concepts like gyroscopic stability, angular momentum, and center of mass. The discussion covers how spinning objects resist forces differently than stationary ones, and they answer listener questions about swimming physics, Jupiter's mysterious interior, and recommended mathematics textbooks.

Introduction to Kendama and Its Physics

Michael introduces Hannah to the kendama, a Japanese skill toy consisting of a wooden stick with cups and a ball attached by string. He explains it's more complex than traditional cup and ball games, with multiple catching options including cups and a spike. The challenge is demonstrating how difficult it is to master despite being easy to understand, setting up a deeper exploration of the physics involved.

  • Kendama is a Japanese cup and ball toy with a stick featuring two side cups, one bottom cup, and a spike
  • The ball can be caught in cups or on the spike through a hole in the ball
  • The toy is described as 'easy to learn, fun to master'
" Every time I try something new there's a little bit of my brain which is like this might be what I was born to do. It's never the thing. It's never been true, but still, every time, every time. "

Adam Savage's Physics-Enhanced Kendama

Michael reveals a custom kendama machined from Delrin plastic by Mythbuster Adam Savage, designed using physics principles to make the trick easier. The heavier ball has the string attached at its exact center to prevent unwanted rotation, and its mass enables gyroscopic stability when spinning. This demonstrates how understanding physics can be applied to practical design improvements, though mastery still requires human skill and practice.

  • The custom kendama is made from Delrin, a machinable dense plastic that's more robust than wood
  • String attachment at the ball's exact center prevents torque and unwanted rotation
  • The heavier ball uses gyroscopic stability to keep the hole facing downward
  • Adam Savage used a special lathe attachment to create perfect spheres and inverse spheres for cups
" Even when you try to hack the physics and make the easiest kendama to catch on a spike, you're still not that good at it. It still takes that human flesh neural network a lot of tries to get the knack of it, to get the physical memory of it. "

📚 4 more sections below

Sign up to unlock the complete summary with all insights, key points, and quotes

Listen on Apple Podcasts More Episodes from The Rest Is Science